Fig. 4From: Metabolite biomarkers of type 2 diabetes mellitus and pre-diabetes: a systematic review and meta-analysisPooled analysis of valine (a), leucine (b), isoleucine (c), phenylalanine (d) and tyrosine (e) in serum and plasma of pre-diabetes and control groups. Studies with several populations comparing patients with pre-diabetes and controls are described by the author name followed by A or B to indicate, for example, subdivision according to sexBack to article page